1. Field of the Invention
This invention relates to exhaust gas recirculation systems for motor vehicle internal combustion engines.
2. Prior Art
Hasegawa et al, U.S. Pat. No. 4,409,948, discloses an EGR control system, comprising an electronic control unit (ECU) 5, and EGR control valves 21, 22. ECU 5 includes a comparator 38 and memories 31, 39. This system automatically corrects a detected zero opening value of the EGR valve, as compared to a valve opening command of value read from a map of required valve opening values for a predetermined period of time.
Fujimoto, U.S. Pat. No. 4,390,001, discloses an EGR system, including a gas recirculation passage 4, a recirculation control valve 5, solenoid valves 7, 8, a control device 9 and a memory device 15. The memory device 15 stores memories of optimum values. The control device 9 receives a signal corresponding to an optimum value of pressure drop P.sub.0 (col. 3, lines 49-55).
Otobe, U.S. Pat. No. 4,665,882, discloses a method of controlling EGR quantity, comprising an EGR valve 16, and a CPU 27 incorporating timers for fault detection, and a RAM 28 and a ROM 29. The ROM 29 stores various maps and tables for calculating the lifting amount of the EGR valve. 16. The October patent teaches a position feedback sensor whereas Applicants teach using a pressure feedback electronic control.
U.S. Pat. No. 4,665,882 compares a desired position to an actual position, and uses lack of achieving the desired position as a fault. Applicants use redundant information available from models of the EGR components to obtain an independent calculation of the expected delta pressure. There is no comparison of desired value to actual value. There is a comparison of model value to actual value.
The '882 patent teaches keeping track of the time at which the error occurs and triggers if this time exceeds a value. It also teaches keeping track of the number of times an error occurs in a given time. There is no provision to count down. Applicants' error counter, active after several gate conditions are achieved, counts a counter up when there is an error, and also counts down when there is not.
However, actual EGR position may not equal the desired position. The most common reason is lack of EGR muscle vacuum at low engine vacuums (high throttle positions). Such a situation can occur at high altitude. Patent '882 teaches a gate on ACT and on ECT. Applicants' invention has neither.
Haka et al, U.S. Pat. No. 4,397,289, discloses an EGR system incorporating a transducer 42 and a control system 72. The control system 72 responds to selected engine operating parameters in order to vary the reference pressure with which the control pressure in the zone 53 is compared.
U.S. Pat. No. 4,834,054, issued to Hashimoto et al, is a fault detector based on EGR temperature The '054 patent has a gate on barometric pressure (BP) In contrast, Applicants' invention teaches a gate on manifold vacuum which is in turn calculated from BP.